Hadley Jons, of Warren just north of Detroit, could be found in contempt when she returns to the Macomb County circuit court Thursday.
Jons, 20, was a juror in a case of resisting arrest. On Aug. 11, a day off from the trial and before the prosecution finished its case, she wrote on Facebook that it was "gonna be fun to tell the defendant they're guilty."
The post was discovered by defense lawyer Saleema Sheikh's son.
Circuit Judge Diane Druzinski confronted Jons the next day and replaced her with an alternate.
"You don't know how disturbing this is," Druzinski said, according to The Macomb Daily.
A message seeking comment was left for Jons on Monday.
"I would like to see her get some jail time, nothing major, a few hours or overnight," Sheikh said. "This is the jury system. People need to know how important it is."
Sheikh's son, Jaxon Goodman, discovered the comment while checking jurors' names on the Internet. He works in his mother's law office.
"I'm really proud of him," Sheikh said.
Without Jons, the jury convicted Sheikh's client of a felony but couldn't agree on a separate misdemeanor charge.